Damascene in semiconductor manufacture is the process of interconnecting metal with the semiconductor device. These metal connections have to be established in a precise manner and interconnecting wires have to be isolated to avoid undesired interaction between the metal wires with other parts of the device.
In the early era of semiconductor manufacture, silica or silicate glasses were used as an insulator. As semiconductor devices became faster and thus smaller, metal connections on a device grew closer requiring that the insulating material (silicates) become thinner. However, build up of charges in the thin layers of insulating material can result in an undesired “crosstalk” between metal connectors. This charge build-up and crosstalk could be avoided by the use of insulating material with a dielectric constant less than 3.9, which are referred to as low k dielectrics.
Chemically, silicates or silicon dioxide are structures where each silicon atom is surrounded by four oxygen atoms. Thereby, the negative charges are predominantly located at the oxygen atoms and positive charges are located at the silicon atom. These charge separations contribute to the relative high dielectric constant of silica. A removal of oxygen in the silicate frame and replacement with groups such as alkyl radicals that do not induce a charge separation between the silicon atom and the alkyl moiety have the result of a lower dielectric constant. Another positive side effect is that these organic silica structures, so called siloxanes are more porous, i.e., less dense than its homologous silica and this contributes to an even lesser dielectric constant. Therefore, some insulation materials used in damascence are low-k Siloxanes, also referred to as SiLK or SiCOH materials.
Dual Damascence is a modified version of the damascene process. Here, prior to the metallization, the semiconductor structure is coated with SiCOH material. Then trenches for the metal connection are etched into the structure using commonly adapted etching methods, such as plasma etching. The etching process has a tendency to damage the SiCOH material resulting in the introduction of oxygen into the SiCOH material, which has the effect of elevating the dielectric constant. The chemical reaction can be described as:

In the past, the damage on the SiCOH material was removed using an aqueous dilution of hydrofluoric acid. However, dilute hydrofluoric acid also etches the low-k material, thus resulting in a widening of the trench. The aqueous solution also attacks other silicon containing parts of the device, e.g. masking layers such as TEOS oxides. Additionally, the penetration of the porous SiCOH material by the aqueous hydrofluoric acid solution may be intensified by capillary forces, thus resulting in a internal corrosion of the low-k material. Furthermore, the use of aqueous solutions may impede the homogenous removal of damage across the silicon wafer, since it is difficult to apply the solution uniformly across the surface. Additionally, in a solution based removal, the surface tension of liquid droplets distributed onto the wafer may result in a non-homogenous trim of the sidewalls of the newly formed trenches.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.